1 /* 2 * Copyright (c) 2011, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 24 25 package jdk.internal.vm.compiler.word; 26 27 // JaCoCo Exclude 28 29 /** 30 * Marker interface for location identities. A different location identity of two memory accesses 31 * guarantees that the two accesses do not interfere. 32 * <p> 33 * Clients of {@link LocationIdentity} must use {@link #equals(Object)}, not {@code ==}, when 34 * comparing two {@link LocationIdentity} values for equality. Likewise, they must not use 35 * {@link java.util.IdentityHashMap}s with {@link LocationIdentity} values as keys. 36 * 37 * @since 1.0 38 */ 39 public abstract class LocationIdentity { 40 41 private static final class AnyLocationIdentity extends LocationIdentity { 42 @Override 43 public boolean isImmutable() { 44 return false; 45 } 46 47 @Override 48 public String toString() { 49 return "ANY_LOCATION"; 50 } 51 } 52 53 private static final class InitLocationIdentity extends LocationIdentity { 54 @Override 55 public boolean isImmutable() { 56 return true; 57 } 58 59 @Override 60 public String toString() { 61 return "INIT_LOCATION"; 62 } 63 } 64 65 /** 66 * Creates a new location identity. Subclasses are responsible to provide proper implementations 67 * of {@link #equals} and {@link #hashCode}. 68 * 69 * @since 1.0 70 */ 71 protected LocationIdentity() { 72 } 73 74 /** 75 * Indicates that the given location is the union of all possible mutable locations. A write to 76 * such a location kill all reads from mutable locations and a read from this location is killed 77 * by any write (except for initialization writes). 78 * 79 * @since 1.0 80 */ 81 public static final LocationIdentity ANY_LOCATION = new AnyLocationIdentity(); 82 83 /** 84 * Location only allowed to be used for writes. Indicates that a completely new memory location 85 * is written. Kills no read. The previous value at the given location must be either 86 * uninitialized or null. Writes to this location do not need a GC pre-barrier. 87 * 88 * @since 1.0 89 */ 90 public static final LocationIdentity INIT_LOCATION = new InitLocationIdentity(); 91 92 /** 93 * Indicates that the given location is the union of all possible mutable locations. A write to 94 * such a location kill all reads from mutable locations and a read from this location is killed 95 * by any write (except for initialization writes). 96 * 97 * @since 1.0 98 */ 99 public static LocationIdentity any() { 100 return ANY_LOCATION; 101 } 102 103 /** 104 * Location only allowed to be used for writes. Indicates that a completely new memory location 105 * is written. Kills no read. The previous value at the given location must be either 106 * uninitialized or null. Writes to this location do not need a GC pre-barrier. 107 * 108 * @since 1.0 109 */ 110 public static LocationIdentity init() { 111 return INIT_LOCATION; 112 } 113 114 /** 115 * Denotes a location is unchanging in all cases. Not that this is different than the Java 116 * notion of final which only requires definite assignment. 117 * 118 * @since 1.0 119 */ 120 public abstract boolean isImmutable(); 121 122 /** 123 * The inversion of {@link #isImmutable}. 124 * 125 * @since 1.0 126 */ 127 public final boolean isMutable() { 128 return !isImmutable(); 129 } 130 131 /** 132 * Returns true if this location identity is {@link #any}. 133 * 134 * @since 1.0 135 */ 136 public final boolean isAny() { 137 return this == ANY_LOCATION; 138 } 139 140 /** 141 * Returns true if this location identity is {@link #init}. 142 * 143 * @since 1.0 144 */ 145 public final boolean isInit() { 146 return this == INIT_LOCATION; 147 } 148 149 /** 150 * Returns true if this location identity is not {@link #any}. 151 * 152 * @since 1.0 153 */ 154 public final boolean isSingle() { 155 return this != ANY_LOCATION; 156 } 157 158 /** 159 * Returns true if the memory slice denoted by this location identity may overlap with the 160 * provided other location identity. 161 * 162 * @since 1.0 163 */ 164 public final boolean overlaps(LocationIdentity other) { 165 return isAny() || other.isAny() || this.equals(other); 166 } 167 }